1. Field of the Invention
The present invention relates to an optical glass; a press-molding glass material and an optical element comprised of the optical glass; and a method of manufacturing an optical element employing the press-molding glass material.
2. Discussion of the Background
In recent years, with the development of highly functional and compact image pickup devices, demand for lenses made of high-refractive-index glass has been rising. High-refractive-index, low-dispersion glasses such as that described in Japanese Unexamined Patent Publication (KOKAI) No. 2007-269584 are known as glass materials for such lenses. Combining a lens comprised of a high-refractive-index, low-dispersion glass with a lens comprised of a high-refractive-index, high-dispersion glass makes it possible to obtain a compact optical system while correcting chromatic aberration. Such lenses occupy extremely important positions as optical elements constituting projection optical systems such as projectors and image pickup optical systems.
Ta2O5 has been employed as a main component in conventional high-refractive-index, low-dispersion glasses (for example, see Japanese Unexamined Patent Publication (KOKAI) No. 2007-269584). That is because Ta2O5 contributes to enhancing devitrification, manufacturing stability, and the like in high-refractive-index, low-dispersion glasses. However, in recent years, the cost of rare metals has been soaring. Among these, the cost of tantalum (Ta) has risen markedly. In addition, its supply on the market is reduced. Thus, in the field of glass manufacturing, there has been a need to reduce the quantity of tantalum employed as a glass starting material.